This application relates to percussion tools of the type which utilize chisel-like bits such as rock drills, paving breakers, chipping hammers and the like. More particularly, the present application relates to the reduction of noise in such types of tools.
Foundry cleaning rooms are extremely noisy places. For example, during periods where a pneumatic hammer and chisel are used to remove sprues, gates, risers and burrs from castings, the noise level in the foundry cleaning room often exceeds 110 dBA, to which OSHA requirements limit employee exposure to 30 minutes a day or less.
Two major noise sources include the pneumatic exhaust from the hammer, and ringing of the casting. Mufflers have been found to be effective in reducing noise due to pneumatic exhaust of the hammer, and sand beds or special holding jigs have had some degree of success in dumping casting ringing.
Applicant has determined that a third major noise source includes the "ringing" of the chisel itself. In addition to the applicant, this potential noise problem has been recognized in an article in the Jan. l959 edition of "Noise Control" magazine and in U.S. Pat. No. 3,662,855. In the "Noise Control" article a proposed solution to chisel ringing comtemplates construction of the entire chisel of a non-metallic material with a fairly high internal damping characteristic. In particular, the author notes that a chisel made of nylon was preferred. In U.S. Pat. 3,662,855, the patentees disclose mounting of a collar of vibration damping material around the tool body for reducing or muffling tool noise, and further indicate that the collar should be located at least around the point of maximum lateral amplitude of the tool body during operation of the machine.